<SEC-DOCUMENT>0000949157-19-000004.txt : 20190103
<SEC-HEADER>0000949157-19-000004.hdr.sgml : 20190103
<ACCEPTANCE-DATETIME>20190103161244
ACCESSION NUMBER:		0000949157-19-000004
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190101
FILED AS OF DATE:		20190103
DATE AS OF CHANGE:		20190103

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Conti Craig C
		CENTRAL INDEX KEY:			0001747814

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34474
		FILM NUMBER:		19505537

	MAIL ADDRESS:	
		STREET 1:		1 S. WACKER DR.
		STREET 2:		SUITE 1000
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CENTURY ALUMINUM CO
		CENTRAL INDEX KEY:			0000949157
		STANDARD INDUSTRIAL CLASSIFICATION:	PRIMARY PRODUCTION OF ALUMINUM [3334]
		IRS NUMBER:				133070826
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1 SOUTH WACKER DRIVE
		STREET 2:		SUITE 1000
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606
		BUSINESS PHONE:		3126963101

	MAIL ADDRESS:	
		STREET 1:		1 SOUTH WACKER DRIVE
		STREET 2:		SUITE 1000
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_154654994647244.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-01-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000949157</issuerCik>
        <issuerName>CENTURY ALUMINUM CO</issuerName>
        <issuerTradingSymbol>CENX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001747814</rptOwnerCik>
            <rptOwnerName>Conti Craig C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1 SOUTH WACKER DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 1000</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP &amp; Chief Financial Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22526</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>45268</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents time vesting performance share units granted to the Reporting Person in connection with the Issuer's 2019-2021 Long-Term Incentive Plan under Rule 16b-3(d), all of which will vest in the ordinary course on the last day of the Plan Period, December 31, 2021.</footnote>
        <footnote id="F2">Includes unvested performance share units granted to the Reporting Person (i) pursuant to Issuer's 2018-2020 and 2019-2021 Long-Term Incentive Plans under Rule 16b-3(d) and (ii) 11,190 time vesting performance share units, 5,776 of which vest in the ordinary course on February 15, 2019 and 5,776 of which vest in the ordinary course on February 15, 2020.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Morgan F. Walbridge, attorney-in-fact for Craig Conti</signatureName>
        <signatureDate>2019-01-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
